The largest single application of lead-acid storage batteries is for the starting, lighting, and ignition of automobiles, trucks and buses. These batteries are charged automatically from a generator driven by the engine while it is running and they supply power for the lights while the engine is shut-down and for ignition and cranking when the engine is started. Lead-acid storage batteries are also widely used in aircraft and boats with virtually unlimited applications also existing in non-motive situations.
Lead-acid batteries are made up of a series of lead-acid cells. A lead-acid cell consists essentially of positive plate containing positive active material such as lead dioxide and negative plates containing negative acid material such as sponge lead immersed in an electrolyte solution typically of dilute sulfuric acid. The respective positive and negative plates are connected in parallel with the power or current output of a cell being determined by the number and size of the plates. The open circuit potential developed between each positive and negative plates is about two volts. Since the plates are connected in parallel, the combined potential for each cell will be also about two volts regardless of the number of plates utilized in the cell. One or more cells are then serially connected to provide a battery of desired voltage. Common low voltage batteries are 6 volt batteries having three serially connected cells, 12 volt batteries with 6 serially connected cells and 24 volt batteries with 12 serially connected cells.
The positive and negative plates are typically oriented vertically in a horizontal stacked relationship. As a result of this vertical orientation, electrolyte stratification commonly occurs vertically along the plate surfaces. This results in diminishing of battery performance. Some attempts have been made to prevent electrolyte stratification, such as stirring of the electrolyte by various mixing systems. These mixing systems are not only cumbersome but are expensive and subject to failure during the life of a particular battery.
Another problem with lead-acid batteries is their limited lifetime due to shedding of the active materials from the positive and negative plates. Pasted plate lead-acid batteries are by far the most common type of lead-acid battery. Typically, a paste of lead oxide is applied to the surfaces of the positive and negative grids. By suitable electric forming, the lead oxide paste on the positive grid is oxidized to lead dioxide while the lead oxide on the negative plate is reduced by suitable electric forming to sponge lead. During continued operation of the lead-acid battery, shedding or flaking of the deposited lead paste is known to occur. The flakes of material fall down between the vertically oriented plates and accumulate on the battery bottom. After a period of time, sufficient flakes accumulate on the battery bottom to short circuit the negative and positive grids resulting in a dead battery cell and shortened battery life.
In the past, lead-acid batteries have been inherently rather heavy due to the use of lead in constructing the plates. Modernly, attempts have been made to produce light-weight lead-acid batteries especially in aircraft, electric cars and other vehicles where weight is an important consideration. Emphasis has been placed on producing thinner plates made from lighter weight materials used in place of and in combination with lead. Although the thinner lightweight plates are beneficial in reducing battery weight, they present problems in regards to providing a cell structure which is sufficiently strong and rigid to prevent structural failure during normal use.
It is therefore desirable to provide an improved low-voltage lead-acid battery which eliminates or substantially reduces common faults, i.e. shedding and electrolyte stratification that contribute to shortened battery life and which is in addition lightweight yet structurally strong.